Lactic acid has a wide range of applications in the industry including foods, medicines, cosmetics, etc. Recently, due to the use of lactic acid as a monomer for polylactic acid, the demand has significantly increased. Methods for producing lactic acid include a traditional chemical synthesis and a biological fermentation process, which has carbohydrates as substrates, and the latter has been favored recently.
Generally, in yeast-based lactic acid-producing microorganisms, lactate dehydrogenase (LDH) and pyruvate decarboxylase (PDC) compete for the use of pyruvate as a substrate. In this regard, it is necessary to minimize the functions of PDC for higher production of lactic acid (LA) by LDH for maximizing the production yield of pyruvate. In Saccharomyces cerevisiae, PDC is present in three different forms of isozymes, i.e., PDC1, PDC5, and PDC6. Therefore, for maximizing lactic acid production, a method for preparing a strain with a simultaneous triple-deletion of PDC1, PDC5, and PDC6 may be used. However, although the inactivation of the PDC activity may increase the yield of lactic acid, it also has disadvantages in that it reduces productivity and that strains cannot be grown smoothly (European Patent No. EP2041264), thus making it difficult to produce a desired amount of lactic acid. Additionally, yeasts, such as the genus Saccharomyces, cannot exactly predict whether a desired amount of lactic acid can be produced by a simple gene manipulation by various cell organelles and various organic systems, unlike in prokaryotes such as bacteria.